Transparent moulding composition of a polycarbonate and a resin

ABSTRACT

A transparent moulding composition comprising a bisphenol polycarbonate having a low refractive index due to a content of alkyl substitution and a rubber and/or a resin.

This invention relates to transparent moulding compounds comprising

a. 10-95% by weight of a transparent aromatic polycarbonate the linear chains of which consist to at least 50% of recurrent structural units of formula (1) ##STR1## in which R₁₋₈ which may be the same or different represent hydrogen or C₁₋₅ alkyl and X may represent a single bond, C₁ to C₁₂ alkylene or alkylidene or ##STR2## if at least one of the R₁₋₈ substituents is a C₁₋₅ alkyl or represents C₆₋₁₂ alkylene or alkylidene if R₁₋₈ is hydrogen and

b. 5-90% by weight of a rubber and/or a transparent resin which contains rubber,

the difference in refractive indices between (a) and (b) being not more than 0.010.

In principle, the invention of these moulding compounds is based on the finding that the polycarbonates defined under (a) have very low refractive indices, so that the requirement of substantially equal refractive index with product (b) is met.

Polycarbonates containing recurrent units of formula (1) are known in the art. They have been described in, inter alia, "Polymer Reviews," Volume 9, Chemistry and Physics of Polycarbonates, by H. Schnell, Interscience Publisher, New York, 1964 and in German Offenlegungsschriften No. 2,063,050; 2,063,052 and 2,211,957 and in German Application No. P 22 10 604.3. They are basically prepared from bisphenols and phosgene in known manner. In addition to bisphenols which, when used in the synthesis of polycarbonates, yield products of formula (1), other bisphenols may also be used for the purpose of the invention to yield copolycarbonates, but these should contain at least 50% of units of formula (1).

Mixtures of polycarbonates which contain units of formula (1) and polycarbonates which do not contain any units of formula (1) are also suitable as constituent (a) of the moulding compounds provided the mixture as a whole contains at least 50% of units of formula (1).

Polycarbonate units of formula (1) may be based on bisphenols such, for example, as the following:

1,1-Bis-(4-hydroxyphenyl)-hexane,

1,1-bis-(4-hydroxyphenyl)-heptane,

1,1-bis-(4-hydroxyphenyl)-octane,

1,1-bis-(4-hydroxyphenyl)-nonane,

1,1-bis-(4-hydroxyphenyl)-decane,

1,1-bis-(4-hydroxyphenyl)-undecane,

1,1-bis-(4-hydroxyphenyl)-dodecane,

2,2-bis-(4-hydroxyphenyl)-4-methylpentane,

2,2-bis-(4-hydroxyphenyl)-hexane,

2,2-bis-(4-hydroxyphenyl)-heptane,

2,2-bis-(4-hydroxyphenyl)-octane,

2,2-bis-(4-hydroxyphenyl)-nonane,

2,2-bis-(4-hydroxyphenyl)-decane,

2,2-bis-(4-hydroxyphenyl)-undecane,

2,2-bis-(4-hydroxyphenyl)-dodecane,

4,4-bis-(4-hydroxyphenyl)-hexane,

4,4-bis-(4-hydroxyphenyl)-heptane,

4,4-bis-(4-hydroxyphenyl)-octane,

4,4-bis-(4-hydroxyphenyl)-nonane,

4,4-bis-(4-hydroxyphenyl)-decane,

4,4-bis-(4-hydroxyphenyl)-undecane, 4,4-bis-(4-hydroxyphenyl)-dodecane,

1,1-bis-(2,5-dimethyl-4-hydroxyphenyl)-ethane,

1,1-bis-(2,5-dimethyl-4-hydroxyphenyl)-isobutane,

2,2-bis-(3-isopropyl-4-hydroxyphenyl)-propane,

2,2-bis-(3-isopropyl-4-hydroxyphenyl)-pentane,

4,4-bis-(3-isopropyl-4-hydroxyphenyl)-heptane,

α,α'-bis-(3-isopropyl-4-hydroxyphenyl)-p-diisopropylbenzene,

α,α'-bis-(3-isopropyl-4-hydroxyphenyl)-m-idisopropylbenzene,

bis-(3,5-diethyl-4-hydroxyphenyl),

bis-(3,5-dimethyl-4-hydroxyphenyl)-methane,

1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-ethane,

1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,

1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-heptane,

1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-dodecane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-butane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-pentane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-4-methylpentane,

2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane,

2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-butane,

3,3-bis-(3,5-dimethyl-4-hydroxyphenyl)-pentane,

3,3-bis-(3,5-dimethyl-4-hydroxyphenyl)-hexane,

4,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-heptane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-octane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-decane,

2,2-bis-(3,5-diethyl-4-hydroxyphenyl)-propane,

-bis-(3,5-diethyl-4-hydroxyphenyl)-methane,

2,2-bis-(3-methyl-5-propyl-4-hydroxyphenyl)-propane,

2,2-bis-(3,5-diethyl-4-hydroxyphenyl)-pentane,

4,4-bis-(3,5-diethyl-4-hydroxyphenyl)-heptane,

α,α'-bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene,

α,α'-bis-(3,5-dimethyl-4-hydroxyphenyl)-m-diisopropylbenzene,

α,α'-bis-(3,5-diethyl-4-hydroxyphenyl)-p-diisopropylbenzene, and

α,α'-bis-(3,5-diethyl-4-hydroxyphenyl)-m-diisopropylbenzene.

Bisphenols which are carrying four alkyl substituents, i.e. in each of the o,o,o',o'-positions to the phenolic hydroxy groups are preferred, especially the following: 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane and 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane.

The following are examples of bisphenols which when used in polycarbonate synthesis do not give rise to carbonate units of formula (1) but can be used for producing copolycarbonates or polycarbonates for the polycarbonate mixtures:

Hydroquinone,

resorcinol,

dihydroxydiphenyls,

bis-(hydroxyphenyl)-alkanes,

bis-(hydroxyphenyl)-cycloalkanes,

bis-(hydroxyphenyl)-sulphides,

bis-(hydroxyphenyl)-ethers,

bis-(hydroxyphenyl)-ketones,

bis-(hydroxyphenyl)-sulphoxides,

bis-(hydroxyphenyl)-sulphones and

α,α'-bis-(hydroxyphenyl)-diisopropylbenzenes

and the corresponding compounds which are alkylated or halogenated in the nucleus but do not give rise to carbonate units of formula (1). These and other suitable aromatic dihydroxy compounds have been described e.g. in U.S. Pat. Nos. 3,028,365; 2,999,835; 3,148,172; 3,271,368; 2,991,273; 3,271,367; 3,780,078; 3,014,891 and 2,999,846 and in German Offenlegungsschrift No. 1,570,603.

The following are particularly preferred:

Bis-(4-hydroxyphenyl)-methane,

2,2-bis-(4-hydroxyphenyl)-propane,

2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane,

2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane and

α,α'-bis-(4-hydroxyphenyl)-p-diisopropylbenzene.

The polycarbonates may, of course, be branched by incorporating small quantities of polyhydroxyl compounds, e.g. 0.05 to 2.0 mols percent (based on the quantity of bisphenols). Polycarbonates of this kind have been described, e.g. in German Offenlegungsschriften No. 1,570,533; 2,116,974 and 2,113,347, in British Patents No. 885,442 and 1,079,821 and in U.S. Pat. No. 3,544,514. The following are some of the polyhydroxyl compounds which are suitable for this purpose: Phloroglucinol, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptene-(2), 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 1,3,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tri-(4-hydroxyphenyl)-phenyl-methane, 2,2-bis-[4,4-(4,4'-dihydroxydiphenyl)-cyclohexyl]-propane, 2,4-bis-(4-hydroxyphenyl-4-isopropyl)-phenol,2,6-bis-(2'-hydroxy-5'-methyl-benzyl)-4-methylphenol, 2,4-dihydroxybenzoic acid, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane and 1,4-bis-(4',40"-dihydroxytriphenyl-methyl)-benzene.

Most of the polycarbonates have molecular weights M_(w), (weight average) of 10,000 to over 200,000, preferably 20,000 to 60,000.

The rubbers for the purpose of this invention may be, for example, polyurethane rubbers ethylene/vinyl acetate rubbers, silicone rubbers polyether rubbers, polyalkenamer rubbers, ethylene/propylene/diene rubbers and so-called diene rubbers, i.e. hompolymers of conjugated dienes which contain from 4 to 8 carbon atoms such as butadiene, isoprene, piperylene and chloroprene, copolymers of such dienes with each other and copolymers of such dienes with other compounds, e.g. with styrene, acrylic or methacrylic compounds (e.g. acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, butyl acrylate or methylmethacrylate) or isobutylene. Rubbers which have a refractive index of n_(D) ²⁰ >1.50 are preferred, e.g. polybutadiene and polyisoprene, copolymers of butadiene and isoprene with styrene and acrylonitrile, and transpolypentenamers.

Transparent resins which contain rubber within the meaning of this invention are either transparent graft polymers into which rubber may have been mixed; transparent mixtures of graft polymers, thermoplastic resins to which rubber may be added or transparent mixtures of thermoplastic resins and rubber.

The total rubber content of the transparent moulding compounds according to the invention is preferably 5 to 40% by weight. It is composed of rubber which has not been grafted and which has been mixed into the transparent moulding compounds and rubber which serves as graft stock for the transparent graft polymers in the mixture.

Transparent graft polymers for the purpose of this invention may be obtained by grafting monomers on rubber.

The monomers used may be styrene and its derivatives, e.g. α-methylstyrene, α-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, p-methylstyrene, 3,4-dimethylstyrene, o- and p-divinylbenzene, p-methyl-α-methylstyrene and p-chloro-α-methylstyrene, and acrylic and methacrylic compounds, e.g. acrylic and methacrylic acid, acrylonitrile, methacrylonitrile, methacrylate, ethylacrylate, n-propyl and isopropyl acrylate, n-butyl and isobutylacrylate, 2-ethylhexylacrylate, methylmethacrylate, ethylmethacrylate, n-propyl and isopropylmethacrylate, n-butyl and isobutyl methacrylate, cyclohexylmethacrylate and isobornyl methacrylate and to which maleic acid anhydride may also be added. Maleic acid anhydride may be used in all cases as additional monomer but not on its own.

The preferred monomers are styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, and methyl and ethyl acrylates and methacrylates. These monomers, as well as the other monomers, may be used alone or mixed with other monomers.

The above mentioned rubbers, for example, may be used as graft stock for producing the transparent graft polymers. Those rubbers which have been mentioned as preferred in the above list are also preferred for this purpose.

Thermoplastic resins is the term used here for those polymers which can be obtained by polymerisation of one or copolymerisation of several of the above mentioned monomers which can also be used for grafting. Here again, those mentioned as preferred monomers are also preferred for this purpose.

The rubbers, thermoplastic resins and graft polymers can be prepared by known methods of radical polymerisation, e.g. by bulk polymerisation or polymerisation in solution, suspension or emulsion or by combined process such as precipitation and bulk/suspension processes. Polymerisation processes carried out with the aid of organometallic mixed catalysts (Ziegler-Natta catalysts) are also known.

The polymer mixtures of this invention may be prepared by various methods. The polymers used as starting materials may all be dissolved together in a solvent or solvent mixture. The polymer mixture can be obtained by precipitating all the polymers together by the addition of a non-solvent or by introducing the solution of polymers dropwise into a precipitating agent or by removal of the solvent by evaporation.

If desired, some polymers may be misxd separately before all the components of the composition are finally mixed. Thus, for example, latices of a resinous copolymer (e.g. styrene/acrylonitrile copolymer) and of a rubber (e.g. butadiene/acrylonitrile copolymer) may be mixed by joint precipitation before they are blended with the polycarbonate to form the final moulding compound.

The polymers used as starting materials may also be mixed in the form of solvent-free melts in mixing apparatus such as extruders, internal kneaders or mixing rollers. Mixing may also be achieved by preparing some polymers which are constituents of the mixture in the presence of other polymers, and this may be carried out in such a way that the first mentioned polymers are at least partly grafted on the high molecular weight polymers in whose presence they are prepared. Thus, for example, styrene may be polymerised by radical polymerisation in the presence of polycarbonate and polybutadiene. This polymerisation may be carried out by various known methods (solution, bead, emulsion or block polymerisation).

The rubber component generally forms a separate phase which is distributed in the polymer matrix. The rubber may be in the form of individual globlets or several globlets agglomerated together or in the form of other regular or irregular particles or conglomerates or particles or also in the form of a network in which other polymers may be embedded. The particle diameter is generally 0.01-20 μm, preferably 0.06-10 μm. The particles may be of one or of more types differing substantially from each other in shape, size and size distribution depending on the method of preparation of the polymer mixture and the choice of its components. Due to differences in the physical make up of the rubber phases, polymer mixtures which contain the same rubber component and also have otherwise the same composition may yet differ from each other in their properties, e.g. their toughness, weld line strength and surface gloss. Thus, for example, the surface gloss of injection mouldings is better if the rubber particles are very small than if they are coarse and, conversely, both toughness and weld line strength are greater in the case of coarser rubber particles than in the case of small particles.

Particularly high weld line strength in observed with rubber particles very irregular in size and shape, as, for example, in polymer mixtures containing non-grafted rubber. Very high weld line strength is also obtained if the rubber component is a graft polymer having particle sizes of 0.8 to 10μ, e.g. graft made by bulk/suspension polymerisation (network structure). Rubber distributed in the form of agglomerates, e.g. agglomerates of very small rubber globlets is also advantageous as it provides for excellent weld line strength and high gloss, provided the agglomerate particle size does not exceed a certain limit.

Total rubber content is also influencing the properties of the polymer mixtures. If two mixtures contain rubber distributed in substantially the same form, toughness and weld line strength increase with increasing rubber content while the modulus of elasticity decreases.

While the rubber component generally forms a separate phase in the polymer mixtures of this invention, the other polymer components of the mixture may form a common phase in which the various polymers are distributed practically in molecular dispersion, or they may form several phases each of which may consist of a mixture of various polymers in practically molecular dispersion.

In order to obtain transparent moulding compounds the rubbers and rubber modified transparent thermoplastic resins must have a refractive index not differing too much from the refractive index of the polycarbonate used; the two refractive indices should generally differ by not more than 0.010 units from each other to guarantee transparency. A moulding compound is defined as being transparent when a layer 1 mm in thickness has a total scattered light transmission Tρ (according to DIN 5036 and DIN 4646) of at least 50. Compounds of which layers 4 mm in thickness have a Tρ of at least 50 are preferred. Those which have Tρ values above 70 in layers 4 mm in thickness are particularly preferred.

Transparent polycarbonate based moulding compounds of the described type have not been described before. Known polymer mixtures of polycarbonates based on bisphenol A and ABS polymers or butadiene/styrene polymers (high impact polystyrene) (see German Pat. No. 1,109,884 and 1,170,141) are not transparent.

Transparent ABS and BS graft polymers are also known but their alloys with bisphenol A based polycarbonate are not transparent because the refractive indices are very different from each other. One well known condition for transparency of polyphasic polymer mixtures such as those mentioned above is substantial equality of the refractive indices of the polymer constituents. It is known to the art that polycarbonates have very high refractive indices as far as transparent thermoplastic resins are concerned. Polycarbonates previously investigated were found to have refractive indices of n_(D) ²⁵ =1.56 to 1.65 (see Kunststoff-Handbuch 1972, Carl hauser Verlag, Munich, Volume VIII). For this reason, it has up to now appeared impossible to produce usable transparent mixtures of polycarbonates and ABS or butadiene/styrene graft polymers. It has now been established that polycarbonates produced from certain bisphenols have extremely low refractive indices, more specifically that refractive indices, can be even below n_(D) ²⁰ =1.56 if the bisphenols contain a high proportion of aliphatic carbon atoms. Another surprising finding was that the refractive indices are especially low in polycarbonates obtained from o,o,o',o'-tetraalkyl substituted bisphenols. Though transparent polymer alloys could, e.g. be obtained from such low refractive index polycarbonates and ABC graft polymers or butadiene/styrene graft polymers by adjusting them to a practically identical refractive index. Alloys which contain polycarbonates based on o,o,o',o'-tetraalkyl substituted bisphenols are particularly remarkable because they are not only highly transparent but also have high softening temperatures and excellent stability to saponification by aqueous alkalies and acids. Compared with the non-transparent mixtures of bisphenol-A-polycarbonates previously known, they have improved compatibility (reflected e.g. in higher yield points σ_(s) in their stress-strain diagram and astonishingly high weld line strength) and higher moduli of elasticity. They also have high impact strength and notched impact strength and high tracking resistane, are easily processed, have high structural viscosity and low susceptibility to stress cracking. The compositions found constitute a new class of transparent synthetic resins with a unique combination of properties not found in other transparent synthetic resins such as polystyrene, polymethylmethacrylate, polyvinyl chloride, transparent ABS and transparent polyamide, polycarbonate and polysulphone.

EXAMPLE 1 Preparation of the polycarbonate component

The polycarbonates shown in the Table were obtained from phosgene and the given bisphenols by interfacial polycondensation, using phenols as chain limiting agents, e.g. as described in polymer reviews, Volume 9, Chemistry and Physics of Polycarbonates by H. Schnell, Interscience Publishers, New York, 1964 and in German Offenlegungsschriften No. 2,063,050 and 2,211,957 and in German Pat. Applications No. P 22 48 817.1 and P 22 04 380.7.

                  TABLE                                                            ______________________________________                                         Polycarbonates                                                                                       Ratio of                                                 Example                                                                               Polycarbonate  constituents                                                                              --M.sub.w                                                                             n.sub.D.sup.20                         ______________________________________                                         a      TMBPA--PC      --         31,000 1.546                                  b      TMBPJ--PC      --         32,000 1.543                                  c      TMBPA--PC/BPA--                                                                               70/20 parts                                                     PC-mixture     by weight  .sup.+ 30,000                                                                         1.554                                  d      TMBPJ/BPA--CPC 75/25 molar                                                                    parts      30,000 1.556                                  e      TMBPA--TCBPA-- 83/17 molar                                                     CPC            parts      31,000 1.553                                  ______________________________________                                          PC = polycarbonate                                                             CPC = copolycarbonate                                                          TMBPA =                                                                        TMBPJ = 2,4bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methyl-butane                  BPA =                                                                          TCBPA = 2,2bis-(3,5-dichloro-4-hydroxyphenyl)-propane                          .sup.+ = molecular weight of BPA--PC (molecular weight of TMBPA--PC as in      Example 1 a)                                                                   --M.sub.w  = molecular weight (weight                                          n.sub.D.sup.20 = refractive index at 20° C.                       

EXAMPLE 2 Preparation of grafting bases

A solution of

w parts by weight of salt-free water,

e parts by weight of the sodium salt of disproportionated abietic acid and

p parts by weight of potassium persulphate

are introduced into a pressure resistant vessel equipped with a stirrer. The air is displaced by introducing nitrogen and the internal temperature of the vessel is adjusted to approximately 60° C.

r parts by weight of dodecylmercaptan are added, followed by

b parts by weight of butadiene and

s parts by weight of styrene.

After termination of polymerisation, small quantities of unreacted butadiene are removed by stirring the latex under reduced pressure. Details of individual runs are tabulated in Table 2.

                  TABLE 2                                                          ______________________________________                                                                               Solids                                   Run                                   content                                  No.  w      e       p   r    b    s   (%)    d.sup.○.sup.2                                                                n.sub.D.sup.20               ______________________________________                                         1    180    3.5     0.3 0.2  100  --  36.9   0.09 1.519                        2    200    3.5     0.3 0.2  65   35  32.9   0.07 1.544                        3    200    3.5     0.3 0.2  45   55  33.0   0.06 1.557                        4    150    3.5     0.3 0.2  70   30  39.7   0.07 1.540                        5     80    1.5.sup.○.sup.1                                                                 0.3 0.35 100  --  56.1   0.39 1.519                        ______________________________________                                          .sup.○.sup.1 0.5 parts were introduced at the beginning of              polymerisation and further 1.0 parts were added in the course of               polymerisation                                                                 .sup.○.sup.2 d = average diameter of latex particles [μm       

EXAMPLE 3 Preparation of graft polymers

The rubber latices of Example 2 were diluted with demineralised water so that they contained

g parts by weight of rubber per

175 parts by weight of water.

0.5 parts by weight of potassium persulphate were added to the water used for diluting the latex. The air was displaced by nitrogen and the reaction mixture heated to 65° C.

2.0 parts by weight of alkylsulphate, dissolved in

25 parts by weight of demineralised water and the total monomer charge tabulated in Table 2 (styrene, methyl methacrylate and acrylonitrile)

per g parts by weight of rubber were introduced through separate inlets within about 4 hours. Stirring was continued for further 2 hours at 65° C. to complete the reaction.

The resulting graft polymer latex was coagulated with 2% of magnesium sulphate solution, the coagulate separated, washed free from salt and dried under vacuum at 70° to 80° C.

                  TABLE 3                                                          ______________________________________                                              Grafting                                                                       base      g-Parts Parts Parts by                                               = latex   by      by    weight of                                                                             Parts by                                                                              refrac-                                  from      weight  weight                                                                               methyl weight of                                                                             tive                                Run  Example 2 of      of    meth-  acrylo-                                                                               index                               No.  Run No.   rubber  styrene                                                                              acrylate                                                                              nitrile                                                                               n.sub.D.sup.20                      ______________________________________                                         6    1         65      35    --     --     1.544                               7    5         48      52    --     --     1.555                               8    1         55      33    --     12     1.542                               9    5         30      52    --     18     1.555                               10   1         34.3    39.3  11.2   15.2   1.544                               11   4         94      6     --     --     1.543                               12   4         65      35    --     --     1.554                               13   4         84      11    --     5      1.545                               14   4         42      42    --     16     1.557                               15   4         60      19.6  15.4   5.0    1.542                               16   4         20.5    50.5   9.5   19.5   1.556                               ______________________________________                                    

EXAMPLE 4 Preparation of thermoplastic copolymers

0.35 parts by weight of potassium persulphate and

0.2 parts by weight of alkyl sulphate are dissolved in

125 parts by weight of demineralised water.

The aqueous solution is heated to 65° C. and the air is displaced with nitrogen. An emulsifier solution of

25 parts by weight of demineralised water and

1.2 parts by weight of the sodium salt of a disproportionated resinic acid

and a monomer mixture of the composition shown in Table 3

are added through two separate inlets over a period of about 4 hours.

Stirring is continued for further 2 hours at 65° C. to complete the reaction. The resulting copolymer latex is coagulated with 2% magnesium sulphate solution, the coagulate is separated off, washed free from salt and dried under vacuum at 70° to 80° C.

                  TABLE 4                                                          ______________________________________                                                       Parts by        Parts by                                                       weight of                                                                               Parts by                                                                              weight of                                             Parts by methyl   weight of                                                                             tertiary                                                                               refractive                               Run  weight of                                                                               meth-    acrylo-                                                                               dodecyl-                                                                               index                                    No.  styrene  acrylate nitrile                                                                               mercaptan                                                                              n.sub.D.sup.20                           ______________________________________                                         17   53       47       --     0.2     1.546                                    18   67       33       --     0.2     1.558                                    19   47.6     40.6       11.8 0.2     1.543                                    20   60       15       25     0.2     1.557                                    ______________________________________                                    

The polycarbonates, rubbers graft polymers and thermoplastic copolymers of the mixtures in Examples 5 to 9 are described in Examples 1 to 4. The polycarbonate and the other polymer components were mixed in a double screw extruder at 220° to 260° C. The polymer strand delivered from the extruder was cooled and granulated

EXAMPLE 5 Mixture of TMBPA-PC and TMBPJ-PC with various graft polymers

TMBPA- and TMBPJ-polycarbonate from Examples 1a and 1b were mixed with various graft polymers from Example 3 in weight ratios of 50:50 and 60:40, respectively, via their solvent-free melts.

                                      TABLE 5                                      __________________________________________________________________________     Example                                                                             TMBPA--PC                                                                             TMBPJ--PC                                                                             Graft polymer                                               5    n.sub.D.sup.20 = 1.546                                                                n.sub.D.sup.20 = 1.543                                                                from Example 3                                                                         refractive                                          Run  (parts by                                                                             (parts by                                                                             Run                                                                               Parts by                                                                            index n.sub.D.sup.20 of                                                               Transparent                                  No.  weight)                                                                               weight)                                                                               No.                                                                               weight                                                                              graft polymer                                                                         mixture                                      __________________________________________________________________________     a    60     --     6  40   1.544  yes                                          b    60     --     10 40   1.544  "                                            c    50     --     13 50   1.545  "                                            d    60     --     8  40   1.542  "                                            e    --     50     8  50   1.542  "                                            f    --     50     11 50   1.543  "                                            g    --     60     15 40   1.543  "                                            __________________________________________________________________________

EXAMPLE 6 Mixtures of copolycarbonates and polycarbonate mixtures with various graft polymers

The TMBPA-PC/BPA-polcarbonate mixture from Example 1c and the TMBPJ/BPA- and TMBPA/TCBPA-copolycarbonates from Examples 1d and 1e were mixed with various graft polymers from Example 3 in weight ratios of 50:50, via their solvent-free melts.

                                      TABLE 6                                      __________________________________________________________________________          TMBPA--PC/BPA--       TMBPA/TCBPA--                                       Example                                                                             PC--       TMBPJ/BPA--CPC                                                                            CPC       Graft polymer from                        6    mixture    n.sub.D.sup.20 = 1.556                                                                    n.sub.D.sup.20 = 1.553                                                                   Example 3                                 Run  n.sub.D.sup.20 = 1.554                                                                    (parts by  (parts by Run                                                                               Parts  Transparent                     No.  (parts by weight)                                                                         weight)    weight)   No.                                                                               by wt.                                                                             n.sub.D.sup.20                                                                    mixture                         __________________________________________________________________________     a    50         --         --        7  50  1.555                                                                             yes                             b    50         --         --        16 50  1.556                                                                             "                               c    --         60         --        9  40  1.555                                                                             "                               d    --         50         --        14 50  1.557                                                                             "                               e    --         --         50        12 50  1.554                                                                             "                               __________________________________________________________________________

EXAMPLE 7 Mixtures of polycarbonates and graft polymers in various proportions

TMBPA- and TMBPJ-polycarbonate and TMBPA/BPA-copolycarbonate from Examples 1a, 1b and 1d were mixed with various graft polymers from Example 3 in various weight ratios, namely 70:30, 50:50 and 40:60 via their solvent-free melt.

                                      TABLE 7                                      __________________________________________________________________________     Example               Graft Polymer                                            7               n.sub.D.sup.20 poly-                                                                 from Example 3                                                                         n.sub.D.sup.20 graft                                                                 Transparent                                Run No.                                                                             Polycarbonate                                                                             carbonate                                                                            Run No. polymer                                                                              mixture                                    __________________________________________________________________________     a    TMBPA--PC  1.546 6       1.544 yes                                        b    TMBPJ--PC  1.543 15      1.543 "                                          c    TMBPJ/BPA--CPC                                                                            1.556 9       1.555 "                                          __________________________________________________________________________

EXAMPLE 8 Mixtures of polycarbonates with rubbers and thermoplastic copolymers

TMBPA- and TMBPJ-polycarbonate and TMBPA/BPA-copolycarbonate from Examples 1a, 1b and 1c were mixed with mixtures of various rubbers from Examples 2 and thermoplastic resins from Example 4, via the solvent-free melts. For details see Table 8.

EXAMPLE 9 Mixtures of polycarbonates graft polymers and thermoplastic copolymers

TMBPJ-polycarbonate from Examples 1b and TMBPA-PC/BPA-PC mixture from Example 1c were mixed with mixtures of graft polymers from Example 3 and thermoplastic copolymers from Example 4, via the solvent-free melts. For details see Table 9.

EXAMPLE 10

Some properties of transparent TMBPA-polycarbonate/graft polymer mixtures of this invention compared with those of BPA-polycarbonate/graft polymer mixtures

The polymer mixtures shown in the Table were prepared from the solvent-free melts as already described above.

                                      TABLE 8                                      __________________________________________________________________________                                       Total mixture                                                       Thermoplastic                                                                             PC/rubber/thermo-                            Example         Rubber copolymer  plastic copolymer                            8    Polycarbonate                                                                             Run    Example 4  Parts by                                     Run No.                                                                             Type    n.sub.D.sup.20                                                                    No. n.sub.D.sup.20                                                                    Run No. n.sub.D.sup.20                                                                    weight                                                                              Transparency                            __________________________________________________________________________     a    TMBPA--PC                                                                              1.546                                                                             2   1.544                                                                             17      1.544                                                                             40/20/40                                                                            yes                                     b    TMBPJ--PC                                                                              1.543                                                                             2   1.544                                                                             19      1.543                                                                             40/20/40                                                                            "                                       c    TMBPJ/  1.556                                                                             3   1.557                                                                             18      1.558                                                                             40/20/40                                                                            "                                            BPA--CPC                                                                  d    TMBPJ/  1.556                                                                             3   1.557                                                                             20      1.557                                                                             40/20/40                                                                            "                                            BPA--CPC                                                                  __________________________________________________________________________

                                      TABLE 9                                      __________________________________________________________________________                                Thermoplastic                                                                             Total mixture                            Example         Graft polymer                                                                             copolymer  PC/rubber/                               9               Example 3  Example 4  thermoplastic                            Run  Polycarbonate                                                                             Run        Run        copolymer                                No.  Type    n.sub.D.sup.20                                                                    No.     n.sub.D.sup.20                                                                    No.     n.sub.D.sup.20                                                                    (parts by wt.)                                                                        Transparency                      __________________________________________________________________________     a    TMBPJ--PC                                                                              1.543                                                                             10      1.544                                                                             19      1.543                                                                             40/40/20                                                                              yes                               b    TMBPA--PC/                                                                             1.554                                                                             12      1.554                                                                             18      1.558                                                                             50/30/20                                                                              "                                      BPA--PC                                                                        mixture                                                                   __________________________________________________________________________

                                      TABLE 10                                     __________________________________________________________________________     Example              % by weight              yield Sapon-                     10   PC/graft % by weight                                                                           polycarbon-              point ifica-                     Run  polymer  rubber in                                                                             ate in mix-                                                                           CSS    E-modulus                                                                            Vicat                                                                               σ.sub.a                                                                        tion Trans-                No.  mixture  mixture                                                                               ture   (cmkp/cm.sup.2)                                                                       (kp/cm.sup.2)                                                                        A (°C.)                                                                      (kp/cm.sup.2)                                                                        stability                                                                           parency               __________________________________________________________________________     a    from Ex. 5a                                                                             26     60     11     15,000                                                                               171  480   a    h                          TMBPA--PC/                                                                     graft                                                                          polymer                                                                   b    from Ex. 5d                                                                             22     60     9      16,500                                                                               178  520   a    h                          TMBPA--PC/                                                                     graft                                                                          polymer                                                                   c    BPA--PC/graft                                                                           26     60     5      13,000                                                                               135  390   d    o                          polymer mix-                                                                   ture, graft                                                                    polymer as in                                                                  Example 5a                                                                d    BPA--PC/graft                                                                           22     60     9      14,600                                                                               138  410   d    e                          polymer mix-                                                                   ture, graft                                                                    polymer as in                                                                  Example 5d                                                                __________________________________________________________________________      Legend:-                                                                       Column 2: Mixtures Example 10c and Example 10d are comparison mixtures fo      comparison with mixtures Example 10a and Example 10b.                          Column 5: CSS = weld line strength, determined as follows: A small             standard test bar is injection moulded by introducing polymer melt from        both ends of the mould so that a weld line is formed in the middle of the      bar; impact strength is then determined in accordance with DIN 53 453.         Columns 6,7 and 8: The Emodulus, heat distortion (Vicat A) and yield poin      (σ.sub.a) of the stressstrain diagram were determined according to       DIN 53 455, DIN 53 460/A and DIN 53 453 respectively.                          Column 9: The saponification stability was tested by immersion for 100         hours in boiling 20% aqueous NaOH and for 500 hours in concentrated            ammonia solution at 25° C. The results were approximately the same      in both media. a = almost unchanged, d = substantially destroyed.              Column 10: h = highly transparent, o =                                         The CSS of the TMBPA--PC used is 13 cmkp/cm.sup.2 and that of the BPA--PC      is 110 cmkp/cm.sup.2.                                                     

We claim:
 1. A transparent moulding compound which comprisesa. 10 to 95% by weight of a transparent aromatic polycarbonate.Iadd., .Iaddend.the linear chains of which consist .[.to.]. .Iadd.of .Iaddend.at least 50% of recurrent structural units of .Iadd.the .Iaddend.formula .[.(1).]. ##STR3## in which R₁ to R₈, which may be the same or different, represent hydrogen or alkyl .Iadd.with the proviso that at least one of the R₁ to R₈ substitutents is an alkyl group .Iaddend.and X represents a single bond, a C₁ to C₁₂ alkylene or alkylidene group or ##STR4## .[.if at least one of the R₁ to R₈ substituents is an alkyl group or represents a C₆ to C₁₂ alkylene or alkylidene group if R₁ to R₈ is hydrogen.]. and b. 5 to 90% by weight of a transparent rubber and/or a transparent resin which contains rubber, the difference in refractive indices between (a) and (b) being not more than 0.010.
 2. A moulding compound as claimed in claim 1 in which, in the general formula (1) of claim 1, R₁ to R₈ represents hydrogen or a C₁ to C₅ alkyl group.
 3. A moulding compound as claimed in claim 1, in which in the general formula (1), R₁, R₂, R₇ and R₈ represent C₁ -C₃ alkyl, R₃, R₄, R₅ and R₆ represent H, and X represents C₁ -C₁₂ alkylene or alkylidene.
 4. A moulding compound as claimed in claim 1, in which the structural units of the formula (1) are based on 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane or 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane.
 5. A moulding compound as claimed in claim 1, in which the polycarbonate (a) contains up to 50% of structural units based on bis-(4-hydroxyphenyl)-methane; 2,2-bis-(4-hydroxyphenyl)-propane; 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane or α,α'-bis-(4-hydroxyphenyl)-p.diisopropylbenzene.
 6. A moulding compound as claimed in claim 1, in which the polycarbonate (a) is branched by the incorporation of small quantities of polyhydroxyl compound.
 7. A moulding compound as claimed in claim 6 in which the polycarbonate contains from 0.05 to 2.0 mols percent of polyhydroxyl compound.
 8. A moulding compound as claimed in claim 1, in which the polycarbonate (a) has a molecular weight of from 10,000 to 200,00.
 9. A moulding compound as claimed in claim 8, in which the polycarbonate (a) has a molecular weight of from 20,000 to 60,000.
 10. A moulding compound as claimed in claim 1, in which the rubber (b) has a refractive index of n_(D) ²⁰ >1.50.
 11. A moulding compound as claimed in claim 1, in which the rubber is polybutadiene, polyisoprene, a copolymer of butadiene or isoprene with styrene and/or acrylonitrile or a transpolypentenamer.
 12. A moulding compound as claimed in claim 1, in which the component (b) is a transparent graft polymer into which rubber has been mixed, a transparent mixture of a graft polymer, a thermoplastic resin and rubber or a transparent mixture of a thermoplastic resin and rubber, said thermoplastic resin being a homopolymer or copolymer of styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, methylacrylate, methylmethacrylate, ethylacrylate or ethylmethacrylate.
 13. A moulding compound as claimed in claim 1, in which the component (b) is a transparent graft polymer or transparent mixture of a graft polymer and a thermoplastic resin, said thermoplastic resin being a homopolymer or copolymer of styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, methylacrylate, methylmethacrylate, ethylacrylate or ethylmethacrylate.
 14. A moulding compound as claimed in claim 1, in which the total rubber content is between 5 and 40% by weight.
 15. A moulding compound as claimed in claim 12 in which the graft polymer is obtained by grafting one or several of the monomers styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, methylacrylate, methylacrylate, ethylacrylate and ethylmethacrylate onto a diene rubber. 